What is generally known as “white” light is actually made from a combination of various wavelengths between about 350 nm and about 750 nm. Depending on the light source, different varieties of wavelengths, of different intensities, may be present. Although a casual observer might not notice the difference between “white” light from one source and “white” light from another source, the specific wavelengths present within the “white” light can have a significant impact on the usefulness of the light for a variety of applications.
Light from the sun is arguably the “gold standard” of illumination. Both the quantity of light provided by the sun, and the spectral distribution of light provided by the sun, vary throughout the day. This variation affects numerous biological processes, for example, the human weight-sleep cycle as well as plant and animal life cycles. Exposure to sunlight is known to have a positive effect on individuals who have been diagnosed with Seasonal Affective Disorder. Additionally, the specific wavelengths within the “white” light present affects the way colors are viewed, affecting not only the appearance of items such as clothing, but also the effectiveness with which tasks such as medical photography may be conducted.
The present inventors have good reason to believe that the ability to control the specific wavelengths present in “white” light has numerous benefits. Examples include sleep research and productivity research, as well as therapy for jet lag and Seasonal Affective Disorder. Agricultural benefits may include enhanced plant growth as well as improved yields during animal and fish farming. Photography, particularly for medical or cosmetic purposes, is often performed under complex, tightly controlled lighting conditions. Furthermore, the manner in which specific colors are presented has clear advertising and commercial benefits.
Many presently available light sources, such as incandescent bulbs, fluorescent tubes, and candles, have limited, fixed spectral characteristics. Although some dimming and spectral change is possible by controlling the power supply and/or utilizing filters, the amounts of change possible is limited, and particularly in the case of filters, results in decreased energy efficiency.
Accordingly, there is a need for a means to accurately reproduce the spectral characteristics of the sun as well as other desired light sources, for both static and dynamic lighting conditions. As one of many examples, such accurate reproduction of light could provide many of the benefits of direct sunlight within indoor environments. There is a further need to permit a user to accurately specify the spectral characteristics of the light to be output. Lastly, there is a need to permit the user to optimize various characteristics of the output light, as well as the specific manner in which the output light accurately mimics light from a target spectrum.